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Key Point: Bragg-Gray cavity theory provides an approximate theory of operation for ionization but requires contradictory assumptions. Spencer-Attix and Burlin theories improve upon this by assuming that low energy electrons deposit their energy locally.

Why is cavity theory necessary?

A cavity theory is used to relate the dose deposited in the cavity (sensitive volume of the detector) to that in the surrounding medium which may be of different atomic number or composition.

What is transient charged equilibrium?

In radiological physics, charged-particle equilibrium (CPE) occurs when the number of charged particles leaving a volume is equal to the number entering, for each energy and type of particle. When CPE exists in an irradiated medium, the absorbed dose in the volume is equal to the collision kerma.

What is electron equilibrium?

Dosimetry. term. Electron. equilibrium is present when, due to ionization. events within and outside this volume elementXChemical base material which cannot be chemically converted …, the same number of electrons with the same energy.

What is Spencer attix cavity theory?

The cavity theory by Spencer and Attix treats the energy deposition in a Bragg-Gray (B-G) cavity (detector). Originally the theory was developed for the case of a B-G detector inside a medium irradiated with photons and assuming electronic equilibrium in the medium at the position of the cavity.

What is stopping power in physics?

Stopping Power is defined by The International Commission on Radiation Units and Measurements or ICRU (Taylor et al., 1970) as the average energy dissipated by ionizing radiation in a medium per unit path length of travel of the radiation in the medium.

What does kerma stand for?

kinetic energy released in materials Acronym for kinetic energy released in materials. Kerma is the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation (neutrons and photons) in a sample of matter, divided by the mass of the sample.

What is energy fluence?

The energy fluence Y describes the energy flow in a photon beam and is. defined as the amount of energy dE crossing a unit area dA: (6.3) The unit of energy fluence Y is MeV/cm2.

Why does pair production occur?

Pair production often refers specifically to a photon creating an electron–positron pair near a nucleus. As energy must be conserved, for pair production to occur, the incoming energy of the photon must be above a threshold of at least the total rest mass energy of the two particles created.

How does Bragg curve occur?

The Bragg Curve falls with increasing energy until a minimum is reached near a velocity of β = 0.9, about 2.2 GeV for protons. LET increases slowly, rising logarithmically for energies above the minimum. At the beginning of each day, the kinetic energy of the NSRL Beam is measured using the Bragg Peak.